Intel® Stratix® 10 General Purpose I/O User Guide

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ID 683518
Date 7/07/2021
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2.3.3. Programmable Open-Drain Output

The programmable open-drain output provides a high-impedance state on output when logic to the output buffer is high. If logic to the output buffer is low, output is low.

You can attach several open-drain outputs to a wire. This connection type is like a logical OR function and is commonly called an active-low wired-OR circuit. If at least one of the outputs is in logic 0 state (active), the circuit sinks the current and brings the line to low voltage.

You can use open-drain output if you are connecting multiple devices to a bus. For example, you can use the open-drain output for system-level control signals that can be asserted by any device or as an interrupt.

You can enable the open-drain output assignment using one of these methods:
  • Design the tristate buffer using OPNDRN primitive.
  • Turn on the Auto Open-Drain Pins option in the Intel® Quartus® Prime software.
You can design open-drain output without enabling the option assignment. However, your design will not use the I/O buffer's open-drain output feature. The open-drain output feature of the I/O buffer provides you the best propagation delay from OE to output.
Note: Do not pull the output voltage higher than the Vi (DC) level. Intel recommends that you perform HSPICE simulation to verify the output voltage in your selected topology. You must ensure the output voltage meets the VIH and VIL requirements of the receiving device.

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